DESCRIPTION (Applicant's Abstract): The goal of this proposal is to understand dimorphism, the developmental switch from the yeast to the filamentous form in fungi and to determine its role in pathogenesis. In Saccharomyces cerevisiae diploid yeast cells develop into a multicellular, pseudohyphal form under conditions of nitrogen starvation. Haploid cells undergo a related process, termed haploid-invasive growth. The analysis of filamentation in the model Saccharomyces system will guide the studies in the less tractable pathogen, Candida albicans. In both fungi the key molecules involved in dimorphism are a family of cell-surface glycoproteins called adhesins or flocculins. In Saccharomyces the MAPkinase and A kinase pathways activate the flocculin FLo1 1, which is required for filamentous growth and adhesion. In the absence of FLo1 1 other members of the flocculin family such as Fig!, and FlolO can be activated to bypass FbolI. Experiments will be carried out to identify the foil independent pathways and to determine whether they are also controlled by the MAPkinase and A kinase pathways. To this end a set of mutants that bypass the requirement for Fbo1 1 (fbp) will be analyzed. The role of an anti-sense RNA from the IME4 gene in controlling the switch between filamentation and sporulation will be determined. The discovery that Saccharomyces Like Candida can stick to plastic is the basis for experiments to uncover the genes and pathways that lead to Saccharomyces biofilm formation. The genetic and physiological requirements for this unusual behavior will be tested by mutant and whole genome array analysis. The goal is to identify the proteins involved in adherence to plastic and to uncover the molecular basis for this adherence. Candida genome arrays will be constructed and used to analyze gene expression changes when this pathogen is co-cultured with cells of the mammalian immune system, both macrophages and neutrophils. Genes identified by this analysis will be deleted and their role in the interaction with the immune system determined. As preliminary experiments indicate a connection between the adhesins, dimorphism, and tissue tropism special attention will be given to this family of genes. The genes uncovered in this analysis are potential targets for the development against this pathogen, which is so devastating to those afflicted with AIDS and other immunocompromised individuals.